U.S. patent application number 15/279597 was filed with the patent office on 2018-03-29 for making channeled electrodes for batteries and capacitors.
The applicant listed for this patent is GM GLOBAL TECHNOLOGY OPERATIONS LLC. Invention is credited to Wentian Gu, Haijing Liu, Zhiqiang Yu.
Application Number | 20180090749 15/279597 |
Document ID | / |
Family ID | 61564389 |
Filed Date | 2018-03-29 |
United States Patent
Application |
20180090749 |
Kind Code |
A1 |
Yu; Zhiqiang ; et
al. |
March 29, 2018 |
MAKING CHANNELED ELECTRODES FOR BATTERIES AND CAPACITORS
Abstract
The anode and/or the cathode of a lithium-transporting or
sodium-transporting electrochemical battery cell or capacitor cell
are formed of small (micrometer-size) electrode material particles
having one or more channels extending through substantially each
electrode particle. The through-channels are formed in the
electrode particles as the particles are being formed from
precursor materials. Channel-forming fibers are mixed with the
electrode precursor materials when the electrode particles are
being formed, and the channel forming material is removed from the
formed electrode particles to leave through channels in the
particles that may subsequently be infiltrated with an electrolyte
for the cell.
Inventors: |
Yu; Zhiqiang; (Shanghai,
CN) ; Liu; Haijing; (Shanghai, CN) ; Gu;
Wentian; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GM GLOBAL TECHNOLOGY OPERATIONS LLC |
DETROIT |
MI |
US |
|
|
Family ID: |
61564389 |
Appl. No.: |
15/279597 |
Filed: |
September 29, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 4/485 20130101;
H01G 11/86 20130101; Y02E 60/13 20130101; C01G 45/1242 20130101;
C01P 2004/62 20130101; H01G 11/24 20130101; Y02T 10/70 20130101;
H01M 2004/027 20130101; H01G 11/32 20130101; H01M 4/505 20130101;
H01G 11/70 20130101; H01G 11/06 20130101; H01G 11/62 20130101; H01M
4/587 20130101; H01G 11/52 20130101; H01M 4/5825 20130101; C01G
53/42 20130101; H01G 11/50 20130101; C01G 51/42 20130101; H01M
4/525 20130101; H01M 10/0525 20130101; Y02E 60/10 20130101; H01G
11/28 20130101; H01M 2004/028 20130101; H01G 11/46 20130101; H01M
10/054 20130101; C01P 2004/61 20130101; H01M 4/583 20130101 |
International
Class: |
H01M 4/1391 20060101
H01M004/1391; H01M 10/0525 20060101 H01M010/0525; H01M 4/133
20060101 H01M004/133; H01M 4/587 20060101 H01M004/587; H01M 4/131
20060101 H01M004/131; H01M 4/485 20060101 H01M004/485; H01M 4/505
20060101 H01M004/505; H01M 4/525 20060101 H01M004/525; H01M 4/58
20060101 H01M004/58; H01M 4/136 20060101 H01M004/136; H01M 4/1393
20060101 H01M004/1393; H01M 4/1397 20060101 H01M004/1397; H01G
11/06 20060101 H01G011/06; H01G 11/62 20060101 H01G011/62; H01G
11/50 20060101 H01G011/50; H01G 11/28 20060101 H01G011/28; H01G
11/86 20060101 H01G011/86; H01G 11/70 20060101 H01G011/70; H01G
11/52 20060101 H01G011/52; H01G 11/24 20060101 H01G011/24 |
Claims
1. A battery or capacitor comprising: an anode formed of particles
of a lithium-containing or sodium-containing active anode material,
a cathode formed of particles of a lithium-containing or
sodium-containing active cathode material, and a liquid electrolyte
containing lithium ions or sodium ions that interact
electrochemically with the anode and cathode materials in the
operation of the battery or capacitor; the particles of at least
one of the active anode material and the active cathode material
containing channels that extend into the particles of electrode
material, or into and through the particles of electrode material,
the channels in the particles of electrode material being sized to
receive a portion of the liquid electrolyte within the interior of
the particles in the electrochemical operation of the battery or
capacitor.
2. A battery or capacitor as stated in claim 1 in which
channel-containing particles of electrode material have largest
dimensions in the range of 0.5 to 30 micrometers.
3. A battery or capacitor as stated in claim 1 in which both the
active anode material particles and the active cathode material
particles contain channels that extend through their particles.
4. A battery or capacitor as stated in claim 1 which is composed as
a lithium-ion battery and in which both the active anode material
particles and the active cathode material particles contain
channels that extend through the particles of the electrode
materials.
5. A battery as stated in claim 4 in which the particles of active
anode material are composed of carbon particles with channels
extending through the carbon particles or particles of lithium
titanate with channels extending through the lithium titanate
particles.
6. A battery as stated in claim 4 in which the particles of active
cathode material are formed of particles of a lithium-containing,
additional metal-containing, and an oxygen-containing compound with
channels extending through the particles.
7. A battery as stated in claim 6 in which particles of active
cathode material are formed of at least one of lithium manganese
oxide, lithium nickel oxide, lithium cobalt oxide, lithium cobalt
aluminum oxide, lithium nickel manganese cobalt oxide, and lithium
iron phosphate.
8. A battery as stated in claim 6 in which particles of active
cathode material are formed of an ionic crystalline compound of a
lithium-metal-oxide in which the metal is one or more of the
elements selected from the group consisting of aluminum, cobalt,
iron, manganese, and nickel.
9. A battery as stated in claim 1 comprising particles of an active
cathode material for the battery, the particles of active cathode
material having a largest dimension of about thirty micrometers and
the particles of active cathode material having channels extending
through the particles of active cathode material.
10. A battery as stated in claim 1 comprising particles of an
active anode material for the battery, the particles of active
anode material being carbon particles having a largest dimension of
about thirty micrometers and the carbon particles of the active
anode material having channels extending through them.
11. A method of making particles of active cathode material or of
active anode material for a battery or capacitor, the as-made
particles of active cathode material or of active anode material
having one or more internal channels for receiving a volume of
liquid electrolyte in a battery or capacitor in which the
channel-containing particles of electrode material are used; the
method comprising: dissolving or dispersing a precursor composition
of the active electrode material in a volume of a liquid;
dispersing fibers in and throughout the volume of the liquid, the
fibers being non-reactive with the precursor composition; forming
particles of the precursor of the active electrode material
composition such that at least a majority of the particles are
formed around at least one of the dispersed channel-forming fibers
and entrain at least one of the channel-forming fibers; calcining
the particles with their entrained channel forming particles to
form particles of the desired active electrode material with
entrained channel-forming fibers; and subjecting the formed
particles of active electrode material with their entrained
channel-forming fibers to chemical and/or thermal processing so as
to remove the entrained fibers from the particles of active
electrode material to thereby leave one or more channels in each
particle of active electrode material for subsequently receiving
the liquid electrolyte.
12. A method as stated in claim 11 in which the formed
channel-containing particles of active cathode material or of
active anode material have maximum particle dimensions of up to
about thirty micrometers.
13. A method as stated in claim 11 which comprises: dispersing
precursor compounds for a lithium-metal-oxide cathode material in
water and mixing the aqueous dispersion with carbon fibers; heating
the water-containing mixture in a sealed container to form
particles of the lithium-metal-oxide cathode material with
entrained carbon fibers extending into, or into and through, the
formed particles; and, thereafter removing the entrained carbon
fibers from the particles of lithium-metal-oxide cathode material
to form the one or more channels in each particle for subsequently
receiving the liquid electrolyte.
14. A method as stated in claim 11 which comprises: mixing
particles of a carbon-forming precursor with channel-forming fiber
or fiber-like particles of a metal, silicon, a metal oxide, or
silicon oxide such that carbon-forming precursor particles entrain
the channel-forming particles, the carbon-forming precursor being
carbonizable to form carbon anode material particles having maximum
particle dimensions up to thirty micrometers; heating the mixture
to carbonize the carbon-forming precursor particles into carbon
anode material particles which entrain the channel-forming
particles; and removing the channel-forming particles from the
carbon anode material particles to form one or more channels in
each carbon particle for subsequently receiving the liquid
electrolyte.
15. A lithium-ion battery or capacitor comprising: an anode formed
of particles of an active anode material composed to receive
lithium from a lithium-containing electrolyte, a cathode formed of
particles of a lithium-containing active cathode material, and a
liquid electrolyte containing lithium ions; the particles of active
anode material and/or particles of active cathode material
containing channels that extend into the particles of the electrode
material, or into and through the particles of the electrode
material, the channels in the particles of electrode material being
sized to receive liquid electrolyte within the interior of the
particles in the electrochemical operation of the lithium-ion
battery or capacitor.
16. A lithium-ion battery or capacitor as stated in claim 15 in
which the channel-containing particles of electrode material have
largest dimensions in the range of 0.5 to 30 micrometers.
17. A battery or capacitor as stated in claim 15 in which the
active anode material particles and the active cathode material
particles contain channels extending through the particles of the
electrode materials.
18. A battery as stated in claim 15 in which the particles of
active anode material are composed of carbon particles with
channels extending through the carbon particles or particles of
lithium titanate with channels extending through the lithium
titanate particles.
19. A battery as stated in claim 19 in which the particles of
active cathode material are formed of a lithium-containing, an
additional metal-containing, and an oxygen-containing compound.
20. A battery as stated in claim 15 in which particles of active
cathode material are formed of at least one of lithium manganese
oxide, lithium nickel oxide, lithium cobalt oxide, lithium cobalt
aluminum oxide, lithium nickel manganese cobalt oxide, and lithium
iron phosphate.
Description
TECHNICAL FIELD
[0001] Particles of active electrode materials for lithium or
sodium batteries or capacitors are formed with channels extending
through their particulate shapes to increase their surface area and
to further increase their contact area with the liquid electrolyte
with which they are infused in the assembled battery or
capacitor.
BACKGROUND OF THE INVENTION
[0002] The material presented as background information in this
section of the specification is not necessarily prior art.
[0003] There are several different types of batteries and
capacitors under current development, and in use, which operate
using a lithium ion-containing or sodium ion-containing liquid or
solid electrolyte. Such batteries include lithium-ion batteries,
sodium-ion batteries, lithium sulfur batteries, sodium sulfur
batteries, lithium ion or sodium ion capacitors, and solid state
batteries using lithium or sodium. In many of these electrochemical
devices the electrode materials (i.e., the anode and cathode active
materials) are prepared in the form of micrometer-size solid
particles of a composition that will intercalate and de-intercalate
lithium ions or sodium ions from and into a suitable electrolyte
material.
[0004] For example, lithium-ion batteries are being adapted for
applications in electrically powered automotive vehicles and in
hybrid vehicles utilizing both an internal combustion engine and an
electrical motor to power the vehicle. Other non-vehicle
applications also utilize lithium or sodium batteries or capacitors
of various combinations of electrode materials for providing
electrical power.
[0005] In a common design of the cells of a lithium-ion battery (or
a lithium-ion capacitor), the electrodes are formed of
micrometer-size particles of active anode material or active
cathode material bonded in a porous layer to one or both sides of a
thin, electrically conductive metal foil. The metal foil serves as
a current collector for the electrode material. In one group of
battery structures, the electrodes are formed as relatively thin
rectangular members. Like-sized anodes and cathodes are assembled
alternately with a thin porous separator layer between each set of
facing porous layers of particulate anode and cathode materials.
The pores of each separator layer and each layer of electrode
material are filled with an electrolyte solution of lithium salt(s)
dissolved in a non-aqueous solvent. The DC potential of each cell
is typically in the range of about two to four volts. The
electrical current producing energy (Wh) of a cell depends largely
on the compositions, shapes, and amounts of electrode materials
that can be accommodated in the preparation and function of each
electrode. There is a continuing need for electrode materials for
lithium batteries and capacitors (and sodium batteries and
capacitors) that can provide increased electric energy and power,
and at lower costs.
SUMMARY OF THE INVENTION
[0006] Practices of this invention are applicable to the making of
channel-containing particulate electrode materials for lithium-ion
batteries, sodium-ion batteries, lithium sulfur batteries, sodium
sulfur batteries, lithium ion capacitors, and sodium ion
capacitors, and solid state batteries utilizing lithium or sodium
as an electrode and electrolyte constituent. But for purposes of
illustration of specific examples, the practice of the invention
will be described in detail in connection with the preparation of
channel-containing particulate anode and cathode materials for use
in a lithium-ion cells and batteries.
[0007] Selected compositions for the anode and cathode of a
lithium-ion battery have typically been formulated in the shapes of
individual solid particles having diameters or largest dimensions,
for example, in the range of about 0.5 to 30 micrometers. The
individual particles each present appreciable surface area with
respect to their three-dimensional shapes for contact with a liquid
lithium ion-containing electrolyte. A group of such particles are
often mixed with a smaller portion of particles of a conductive
material, such as carbon black or other conductive carbon
particles, and bonded, e.g., with a relatively small quantity of a
suitable polymeric binder material, as a porous particulate layer
of generally uniform thickness to a flat major surface of a metal
foil current collector. Alternating porous particulate layers of
anode material and cathode material with an interposed thin porous
layer of separator material are stacked or rolled to form cells of
the lithium-ion battery. The layers of electrode materials and the
intervening separator are infiltrated with a liquid lithium
ion-conducting electrolyte, typically formed of a solution of a
lithium salt in a non-aqueous solvent. The electrochemical
efficiency of the cell or grouping of cells is dependent in part on
good contact between lithium ions in the liquid electrolyte and the
respective surfaces of the particles of anode material and
particles of cathode material.
[0008] In accordance with practices of this invention, the
particles of cathode material are initially formed with one or more
channels extending through substantially each particle; each
channel having an opening at one surface location and extending in
a generally straight line to an opening at a second surface
location. And the anode particles are also formed with comparable
through-channels extending through substantially each of the anode
particles. The contribution of such through-channels in each of the
anode material particles and each of the cathode material particles
is to increase the accessible contact area of each particle with
the electrolyte liquid and to increase the transport of the
electrolyte ions in the respective electrode particles and through
the layers of the respective electrode particles.
[0009] The cathode of a lithium-ion cell is the positive electrode
during discharge of the cell. Cathode particles for lithium-ion
batteries are often composed of lithium-containing, one or more
additional metal-containing, and oxygen-containing compounds such
as lithium manganese oxide, lithium nickel oxide, lithium cobalt
oxide, lithium cobalt aluminum oxide, lithium nickel manganese
cobalt oxide, lithium iron phosphate, and other
lithium-metal-oxides, and lithium-metal-phosphates. Many of these
compounds are used commercially and prepared in substantial
amounts. Procedures are known for synthesizing substantially all
such compounds with useful crystal structures for the intercalation
and de-intercalation of lithium (or sodium). Such
lithium-containing compounds may be formed, for example, by
dissolving selected precursor compounds in water and precipitating
the small crystalline particles of the desired compound from the
aqueous solution of precursors. In other practices, the lithium and
oxygen containing cathode compound material may be formed by known
sol-gel processes, or known hydrothermal/solvothermal processes.
The lithium-containing cathode compound is formed or synthesized by
a suitable, known method and then separated as a crystalline
material from the liquid medium or other medium in which it was
formed.
[0010] However, before the desired lithium-containing compound is
precipitated (or otherwise formed in the solid state), a suitable
amount of small (nanometer-size or lower micrometer size)
channel-former fibers are dispersed in the aqueous solution or
other reaction medium. Suitable channel-formers for the particles
of lithium-containing cathode material include carbon fibers (with
or without branches), carbon nanotubes, vapor grown carbon fibers
(VGCF), carbon powder, polymer fibers, SiO.sub.2 fibers, or metal
or metal oxide fibers. Such channel-former materials suitably have
lengths in the range of 100 nanometers to 10 micrometers and
complementary smaller diameters in the range of ten nanometers to
one micrometer. The surfaces of the channel-formers may be thinly
coated with a surfactant to enhance dispersion of the fibers in the
solution or other reaction medium from which the cathode compound
is formed. Typically, precursor articles of the desired cathode
material are formed on and around the channel-forming fibers such
that the intended channel-forming fibers extend into the precursor
particles or, preferably, into and through the precursor particles
from one surface region to an opposing surface region. Calcination
of the particles of precursor material leads to the formation of
particles of the electrode material which still contain the
channel-forming fibers. The calcination step may also promote
removal of the fibers from the bodies of the formed electrode
particles leaving channels extending through the particles, i.e.,
from one surface of the particle to an opposing surface. The
channels are intended to subsequently accommodate a small fluid
volume of liquid electrolyte.
[0011] Accordingly, in a specific example, particles of lithium
manganese oxide, LiMn.sub.2O.sub.4 in spinel ionic crystal
structure (LMO), or precursor materials for lithium manganese
oxide, may be precipitated from an aqueous solution of lithium
nitrate and manganese nitrate, for example by the addition of
lithium hydroxide, onto small carbon fibers dispersed uniformly in
the aqueous medium. In a preferred practice, each precipitated
particle of lithium manganese oxide precursor (e.g., a deposit of
lithium hydroxide and manganese hydroxide ((Mn(OH).sub.2), forms on
one or more of the dispersed carbon fibers. The precipitated carbon
fiber-containing LMO precursor particles are separated from the
aqueous medium, washed if necessary, and dried. The dried LMO
precursor particles are then heated in air (annealed) at a selected
temperature (e.g., in the range of 500.degree. C. to 1500.degree.
C. for the purpose of crystallizing LMO and oxidizing the entrained
carbon fibers to carbon dioxide. Following the removal of the
channel-forming carbon fibers as carbon dioxide, the LMO particles
are now each characterized by the presence of one or more channels
through their particulate shapes. The channel-containing LMO
particles of cathode material are then suitable for use as the
cathode material in a lithium-ion cell or battery of cells in which
the electrode material is intended to be contacted by and to
receive liquid electrolyte within its channel or channels.
[0012] The anode of a lithium-ion cell is the negative electrode
when the cell is being discharged to produce a flow of electrons in
an external resistive circuit. Channel-containing, anode particles
may be prepared in a manner analogous to the above-described
description of the preparation of cathode particles. Anode
particles for lithium-ion cells and batteries (and capacitors) are
often formed of graphite, other forms of carbon, or lithium
titanate (Li.sub.4Ti.sub.5O.sub.12). In the event that the selected
anode material is lithium titanate particles, they may be prepared
with through-channels in a practice utilizing carbon fibers like
that described above in this specification for the preparation of
LMO cathode particles. Graphite and other carbon anode materials
are often prepared from a selected carbon precursor such as a
carbon-based oil or pitch. In accordance with practices of this
invention a selected volume or mass of carbon particle precursor is
mixed with fiber-like particles of a metal, metal oxide, metal
carbide, or of SiO.sub.2. Such channel-forming fibers are
preferably sized like the carbon fibers described in an above
paragraph of this specification.
[0013] The volume of the mixture of carbon particle precursor and
channel-forming fibers is heated in a known, presently-used
reaction medium (such as an inert liquid medium) such that small
individual particles or droplets of fiber-filled carbon particle
precursor are melted and initially formed. The melted carbon
precursor particles are heated to temperatures in the range of
1500.degree. C. to 3000.degree. C. and progressively carbonized
while they continue to contain their channel-forming fibers. When
suitable carbon anode particles have been formed by the
carbonization reaction, the carbon particles are cooled and ready
for removal of their entrained channel formers. In many embodiments
of the invention, the metallic or silicon-containing
channel-formers are readily leached from the carbon particles using
an acid or other suitable solvent. Following the removal of the
channel-forming fibers, the carbon particles are now each
characterized by the presence of one or more channels through their
particulate shapes. The channel-containing carbon particles of
anode material are then suitable for use as the anode material in a
lithium cell or battery of cells.
[0014] A suitable quantity of channeled cathode particles may be
used in the preparation of a porous cathode layer for a lithium or
sodium battery or capacitor and a suitable quantity of channeled
anode particles may be used in the preparation of a complementary
porous anode for a lithium or sodium battery or capacitor.
Alternatively, a cell may be formed using channeled cathode
particles in combination with conventional (non-channeled) anode
particles or vice-versa.
[0015] Other objects, embodiments, and examples of the practice of
this invention will be apparent from a detailed description of
illustrative embodiments which follow in this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is an enlarged schematic illustration of a
spaced-apart assembly of three solid members of a lithium-ion
electrochemical cell. Small portions of the porous anode and
cathode layers are broken out and enlarged to show the
through-channels formed in the particles of anode material and the
particles of cathode material. The through-channels in the
particles of anode and cathode materials are illustrated
schematically, and intended to show a few channels in each particle
that extend from a surface region of the particle through the
particle to another portion of the surface of the particle. The
number of channels formed in an electrode particle depends on the
practice of the process by which it is formed. The solid anode,
opposing cathode, and interposed separator are shown spaced apart
to better illustrate their structure. The drawing does not
illustrate the electrolyte solution which would fill the pores of
the electrode layers and the separator when those members are
assembled in a pressed-together arrangement in an operating
cell.
[0017] FIG. 2 is an enlarged, broken-out, schematic illustration of
a porous layer of particles of cathode material with
through-channels formed in the particles of cathode material and
bonded to an aluminum foil current collector, and a porous layer of
anode particles, each containing channels, and bonded to a copper
current collector foil. Again, the through-channels in the
particles of anode and cathode materials are illustrated
schematically, and intended to show a few channels in each particle
that extend from a surface region of the particle through the
particle to another portion of the surface of the particle. The
number of channels formed in an electrode particle depends on the
practice of the process by which it is formed. The unbounded sides
of the porous electrode layers are pressed against opposite sides
of a co-extensive porous polymeric separator member.
[0018] FIG. 3 is a schematic cross-sectional side view of an anode
current collector foil coated on both major sides with a mixture of
active anode material particles with through-channels, a cathode
current collector foil coated on both sides with a mixture of
active cathode material channel-containing particles for a
lithium-ion battery cathode. The two electrodes are rectangular in
shape (not visible in this side view, but as illustrated in FIG.
1). The opposing major faces of the anode and cathode are
physically separated by a porous rectangular polymer separator
layer wound from the full outer surface of the cathode, around one
edge of the cathode to fully cover the inner face of the cathode
and separate it from the adjoining face of the anode, around the
edge of the anode to cover the outer face of the anode. The two
electrodes with their channel-containing particulate electrode
materials are placed within a closely spaced pouch container. The
pouch contains a non-aqueous electrolyte solution which permeates
and fills the pores of the separator and of the respective active
anode and cathode coating layers. The respective current collector
foils have uncoated tabs extending up from their top sides and
through the top surface of the pouch container.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0019] FIG. 1 is an enlarged schematic illustration of a
spaced-apart assembly 10 of an anode, cathode, and separator of a
lithium-ion electrochemical cell. The three solid members are
spaced apart in this illustration to better show their structure.
The illustration does not include an electrolyte solution whose
composition and function will be described in more detail below in
this specification.
[0020] In FIG. 1, the anode, the negative electrode during
discharge of the cell, is formed of uniformly-thick, porous layers
14 of carbon (e.g., graphite) particles, the majority of the carbon
particles being formed with through-channels, and deposited and
resin bonded on both major surfaces of a relatively thin,
conductive metal foil current collector 12. For example, the carbon
anode particles, and any conductive carbon particles or other
additives, may be resin-bonded, for example, to the current
collector by preparing a slurry of the particles in a solution of
polyvinylidene difluoride (PVDF) dispersed or dissolved in
N-methyl-2-pyrrolidone and applying the slurry as a porous layer (a
precursor of anode layer 14) to the surfaces of the current
collector 12 and removing the solvent. When the anode is formed of
channel-containing carbon particles, the negative electrode current
collector 12 is typically formed of a thin layer of copper foil.
The thickness of the metal foil current collector is suitably in
the range of about ten to twenty-five micrometers. The current
collector 12 has a desired two-dimensional plan-view shape for
assembly with other solid members of a cell. Current collector 12
is illustrated as having a major surface with a rectangular shape,
and further provided with a connector tab 12' for connection with
other electrodes in a grouping of lithium-ion cells to provide a
desired electrical potential or electrical current flow.
[0021] As stated, deposited on both major faces of the negative
electrode current collector 12 are thin, porous anode layers 14 of
channel-containing carbon particles. In accordance with this
disclosure, the negative electrode material is typically
resin-bonded particles of channel-containing carbon particles which
may include interspersed activated carbon particles providing
enhanced electron conductivity. As illustrated in FIG. 1, the
layers of anode material 14 are typically co-extensive in shape and
area with the main surface of their current collector 12. In FIG. 1
a broken out portion of one of the anode layers 14 is enlarged to
schematically illustrate individual carbon particles 13 with
through-channels 15. In this broken out view only the
channel-containing carbon particles are illustrated. No binder
resin or conductive carbon particles are shown to simplify the
illustration of the channel-containing 15, carbon anode particles
13.
[0022] The particulate electrode material has sufficient porosity
to be infiltrated by a liquid, non-aqueous, lithium-ion containing
electrolyte. In accordance with embodiments of this invention, the
thickness of the rectangular layers of carbon-containing negative
electrode material may be up to about two hundred micrometers so as
to provide a desired current and power capacity for the anode.
[0023] A cathode is shown, comprising a collector foil 16 (which is
positively charged during discharge of the cell) and on each major
face, a coextensive, overlying, porous layer 18 of a resin-bonded
mixture of particles of through channel-containing, active cathode
material. For example, the selected cathode material may be
particles of lithium manganese oxide (LiMn.sub.2O.sub.4, spinel
structure), the majority of the LMO particles being formed with
through channels in accordance with this invention. A broken-out
portion of one of the layers 18 of active cathode material is
enlarged to schematically illustrate particles of cathode material
17 with their through-channels 19. No binder resin or conductive
particles are shown in this enlarged simplified illustration.
[0024] Positive current collector foil 16 may be formed of
aluminum. Positive current collector foil 16 typically also has a
connector tab 16' for electrical connection with other electrodes
in a grouping of like lithium-ion cells or with other electrodes in
other cells that may be packaged together in the assembly of a
lithium-ion battery. The cathode collector foil 16 and its opposing
coated porous cathode material layers 18 of channel-containing LMO
particles are typically formed in a size and shape that are
complementary to the dimensions of an associated negative
electrode.
[0025] In the illustration of FIG. 1, the two electrodes are
substantially identical in their shapes and assembled in a
lithium-ion cell with a major outer surface layer of the anode
material 14 facing a major outer surface layer of the cathode
material 18. The thicknesses of the rectangular layers of positive
electrode material 18 are typically determined to complement the
anode material 14 in producing the intended electrochemical
capacity of the lithium-ion cell. The thicknesses of current
collector foils are typically in the range of about 10 to 25
micrometers. And the thicknesses of the respective electrode
material layers are typically up to about 200 micrometers.
[0026] A thin porous separator layer 20 is interposed between a
major outer face of the negative electrode channel-containing
particulate material layer 14 and a major outer face of the
positive electrode channel-containing particulate material layer
18. A like separator layer 20 could also be placed against each of
the opposite outer layers of negative electrode material 14 and the
opposite outer layer of positive electrode material 18 if the
illustrated individual cell assembly 10 is to be combined with like
assemblies of cell members to form a battery with many cells, for
example, many stacked or rolled cells.
[0027] In many battery constructions, the separator material is a
porous layer of a polyolefin, such as polyethylene (PE) or
polypropylene (PP). Often the thermoplastic material comprises
inter-bonded, randomly oriented fibers of PE or PP. The fiber
surfaces of the separator may be coated with particles of alumina,
or other insulator material, to enhance the electrical resistance
of the separator, while retaining the porosity of the separator
layer for infiltration with liquid electrolyte and transport of
lithium ions between the cell electrodes. The separator layer 20 is
used to prevent direct electrical contact between the facing
negative and positive electrode material layers 14, 18, and is
shaped and sized to serve this function. In the assembly of the
cell, the facing major faces of the channel-containing electrode
material 14, 18 are pressed against the major area faces of the
separator membrane 20. A liquid electrolyte is typically injected
into the pores of the separator and electrode material layers.
[0028] The electrolyte for the lithium-ion cell is often a lithium
salt dissolved in one or more organic liquid solvents. Examples of
suitable salts include lithium hexafluorophosphate (LiPF.sub.6),
lithium tetrafluoroborate (LiBF.sub.4), lithium perchlorate
(LiClO.sub.4), lithium hexafluoroarsenate (LiAsF.sub.6), and
lithium trifluoroethanesulfonimide (LiTFSI). Some examples of
solvents that may be used to dissolve the electrolyte salt include
ethylene carbonate, dimethyl carbonate, methylethyl carbonate, and
propylene carbonate. There are other lithium salts that may be used
and other solvents. But a combination of lithium salt and solvent
is selected for providing suitable mobility and transport of
lithium ions in the operation of the cell. The electrolyte is
carefully dispersed into and between closely spaced layers of the
electrode elements and separator layers. In accordance with this
invention, the electrolyte is also dispersed in the channels of the
particles of the respective electrode materials. The electrolyte is
not illustrated in the drawing figure, but it is schematically
illustrated in FIG. 3.
[0029] FIG. 2 is an enlarged schematic illustration of a porous
anode layer 214 bonded one of its sides to one face of a copper
current collector foil 212. The other major face of porous anode
layer 214 is placed coextensively against one side of a porous,
electrically insulating separator 220. Placed against the other
face of separator 220 is one side of a porous cathode layer 218.
The second side of porous cathode layer 218 is bonded to an
aluminum current collector foil 216.
[0030] As illustrated schematically in FIG. 2, porous anode layer
214 comprises micrometer-size particles of active anode material
213. Each of the micrometer-size particles 213 (or at least a
majority of the anode material particles) is formed with channels
215 preferably extending through their particulate bodies 213. As
suggested above in this text, the particles of active anode
material 213 may be formed of graphite or other suitable
lithium-ion-intercalating form of carbon. Several other suitable
anode materials are listed above in this specification. In FIG. 2,
the particles of anode material 213 are illustrated as being
somewhat spherical, but irregular in shape. The anode materials may
have other shapes, but it is preferred that the particles be shaped
for mixing and close packing while leaving suitable pore space for
infiltration with the liquid electrolyte which is introduced into
an assembled cell.
[0031] Porous cathode layer comprises a porous layer 218 of
micrometer-size particles of active cathode material 217, formed to
contain through-channels 219 and resin-bonded as a porous layer 218
to an aluminum current collector foil 216. As suggested above in
this text, the particles of active cathode material 217 may be
formed, for example, of LMO (lithium manganese oxide). Several
other suitable cathode materials are listed above in this
specification. In FIG. 2, the particles of channel-containing 219,
cathode material 217 are also illustrated as being spherical. But
the cathode materials may have other shapes suitable for mixing and
close packing while leaving suitable pore space for infiltration
with the liquid electrolyte which is introduced into an assembled
cell.
[0032] FIG. 3 presents a simplified, schematic, cross-sectional
side-view of an assembly 300 of a single cell 301 of lithium-ion
battery electrode materials assembled into a polymer-coated,
aluminum foil pouch 324. The cell 301 with electrode materials
comprises a cathode current collector foil 316 coated on both major
sides with a porous layer of active through-channel-containing
cathode material particles 318 for a lithium-ion battery cathode.
Cell 301 also comprises an anode current collector foil 312 coated
on both sides with a porous layer of through channel-containing
active anode material particles 314 for a lithium-ion battery
anode. The two electrodes are rectangular in shape (like those
illustrated in FIG. 1). The opposing major faces of the anode and
cathode are physically separated by porous rectangular polymer
separator layer 320 which in some embodiments may be wound from the
full outer surface of the cathode, around one edge of the cathode
to separate the adjoining face of the anode and the cathode, around
the edge of the anode to cover the outer face of the anode. The two
electrodes with their through channel-containing electrode
materials are placed within a closely spaced pouch container 324.
The pouch 324 contains a non-aqueous electrolyte solution 322 which
permeates and fills the pores of the separator 320 and of the
respective active anode and cathode coating layers 314, 318. The
respective current collector foils 312, 316 have uncoated tabs
312', 316' extending up from their top sides and through the top
surface of the pouch container 324.
[0033] At least one of the anode and cathode of each lithium-ion
cell (or sodium cell or lithium or sodium capacitor), and
preferably both, are formed by preparing channel-containing
particles of suitable electrode material. In the preparation of a
resin-bonded porous electrode layer, the individual
channel-containing particles are coated or otherwise suitably
combined with a suitable amount of a bonding material and in a
manner such that the particles may be suitably bonded in a porous
layer of electrode material without covering the through-channels
in the electrode particles and losing the benefit of their presence
in a cell or battery (or capacitor). For example, the
channel-containing particles of active electrode material may be
dispersed or slurried with a solution of a suitable resin, such as
polyvinylidene difluoride dissolved in N-methyl-2-pyrrolidone, and
spread and applied to a surface of a current collector in a porous
layer. Other suitable binder resins include carboxymethyl
cellulose/styrene butadiene rubber resins (CMC/SBR). The binders
are not electrically conducive, which is a further reason that they
should be used in a minimal suitable amount to obtain a durable
coating of porous electrode material and without covering the
channel openings in the surfaces of the particles of electrode
material. After the bonding action or reaction is completed, a
porous layer of electrode material particles is formed on the
current collector. The electrode material particles (and conductive
carbon particles or other additives) are bonded to each other as a
porous layer, and one side of the layer is bonded to the current
collector.
[0034] It is preferred that the porous layers of electrode
materials have a generally uniformly distributed porosity and total
pore volume produced by the pore spaces between the
channel-containing particles of electrode material. Both the
channels formed in the electrode material particles and the spaces
between the particles contribute open volume for infusion with a
liquid electrolyte. Such porosity and channels volume permits the
electrode layers to be suitably generally uniformly infiltrated
with a volume of suitable liquid electrolyte. The interaction of
the combination of the volume of liquid electrolyte material and
the channel-containing particles of electrode materials produce the
desired functions of the electrodes. In most electrode structures,
the total channel volume and pore volume is suitably in the range
of about 15 to 50 percent of the superficial outline volume of the
applied electrode layer.
[0035] As illustrated in FIG. 3, each anode layer 314 or cathode
layer 318 has one surface bonded to its current collector 312, 316
and the other surface lies against an adjacent surface of a porous
separator 320. The volume and nature of the total number of
individual pores between the channel-containing particles of the
electrode is to permit an inserted liquid electrolyte 322 to
permeate the electrode layers 314, 318 from the separator side to
the current collector side of the anode or cathode. Lithium ions
must be accessible to the surfaces of the particles of the anode or
cathode material and the channels formed within them.
[0036] As stated, in general, the method aspect of this invention
provides active anode material particles with through-channels
within the formed active anode particles and/or, separately, active
cathode material particles with through-channels within the cathode
material particles. Suitable precursor particles of a selected
anode or cathode material are formed in a manner in which the
precursor material(s) are deposited or otherwise formed around
nanometer size or lower micrometer size fibers (or tubes or rods or
the like) of a suitable composition. The fibers are initially sized
so as to extend through the droplets or particles of precursor
material which entrains them. The fibers are used as
channel-formers with respect to the enclosing particulate or
droplet precursor(s) of the electrode material. Small droplets or
particles of the precursor material(s), with the enclosed fibers,
are heated in an atmosphere suitable for converting the precursor
material(s) into particles of the desired active electrode
material. Concurrently with, or subsequently to, the formation of
the active electrode material, the entrained, channel-forming
fibers are chemically removed from within the particles of active
electrode material. The majority or all of the active electrode
material particles now contain one or more channels extending
through some portion of the electrode particles. Thus, when the
particles are formed as a porous electrode layer for a battery or
capacitor, and then infiltrated with a liquid electrolyte, the
electrolyte flows in the pores between the particles and in the
channels within the particles.
[0037] It is recognized that there are many different chemical or
material compositions of electrode materials for the lithium-using
and sodium-using electrode materials used in such batteries and
capacitors. Those electrode materials in present use have known
manufacturing processes for utilizing precursor materials in the
synthesis or preparing of the electrode materials in particle form
for subsequent processing into porous particulate electrode layers.
And newly identified electrode materials will have suitable methods
for their preparation into usable particulate forms. The processes
of this invention can use such known precursor processing in the
formation of electrode particles with internal through-channels for
increasing the surface areas of the particles for contact with a
liquid electrolyte solution to be used in the assembled battery or
capacitor.
[0038] Two illustrative examples follow in which the use of
precursors to form channel-containing electrode materials for
batteries or capacitors is presented.
[0039] In the above Summary portion of this specification, the
preparation of channeled lithium manganese oxide particles as
active cathode material particles and the preparation of channeled
carbon particles as active anode particles, both for lithium-ion
battery cells, are described. Following are further descriptions of
these processes utilizing known precursor materials for each
electrode material.
[0040] First, channel-containing lithium manganese oxide particles
may be prepared as follows. An aqueous solution of manganese
nitrate (Mn(NO.sub.3).sub.2) and a hydrogen peroxide
(H.sub.2O.sub.2)-based solution of LiOH are prepared and mixed.
Vapor grown carbon fibers (VGCF) are dispersed in the mixed
solution. The mixture is then heated in a sealed (but shaken)
hydrothermal reactor at 110.degree. C. to 180.degree. C. over a
period of eight to forty-eight hours. During this pressurized
heating process, small particles of crystallized LiMn.sub.2O.sub.4
(LMO) are formed and precipitated on the VGCF fibers. At the
completion of the reaction, the micrometer-size LMO particles with
their entrained carbon fibers are separated from the aqueous medium
and dried.
[0041] The LMO particles with their entrained carbon fibers are
then calcined in air at 500-600.degree. C. for the purpose of
progressively oxidizing the entrained carbon fibers to carbon
dioxide to achieve complete removal of the carbon fibers from the
LMO particles. At the completion of the calcining step and with
cooling of the particles, the LMO particles are found to have one
or more channels distributed through their particulate shapes.
[0042] Second, channeled carbon particles of anode material may be
prepared as follows. Petroleum coke or pitch, may be used as the
precursor material for the production of the channeled carbon
particles as active anode material. Petroleum coke or pitch
contains approximately 10-20% volatile components in the form of
water and volatile organic matter. Before this carbon precursor is
suitable for the manufacture of synthetic carbon, its volatile
components must be removed by a calcining process, which involves
heating the coke or pitch to a high enough temperature
(1250-1350.degree. C.) to volatize, vaporize, or burn off any
volatile components. Once the calcining process is completed the
calcined and melted petroleum coke or pitch is be mixed with
suitable, commercially available, micrometer-size fibers or
elongated particles of a metal oxide or silicon-containing
channel-former (such as Al.sub.2O.sub.3 or SiO.sub.2). The mixture
of hot molten pitch and oxide fibers is suitably kneaded and shaped
into small droplets.
[0043] After the kneading and shape-forming, the fiber-filled
carbon precursor mixture is heated to a temperature higher than
about 2800.degree. C. and progressively carbonized while the
droplets or particles continue to contain their channel-forming
fibers. The high temperature carbonization process produces a
reducing atmosphere. During the carbonization process, the
channel-forming fibers are partially reduced to Al or silicon in
the reduction atmosphere. Finally, the resulting carbon particles
are cooled and ready for removal of their entrained channel formers
by hydrochloric acid or hydrofluoric acid. Following the removal of
the channel-forming fibers, the carbon particles are now each
characterized by the presence of one or more channels through their
particulate shapes. The channel-containing carbon fibers are
suitable for use in a range of lithium-using or sodium-using
batteries and capacitors.
[0044] Thus, available precursor materials for many known anode and
cathode materials may be adapted for deposition of the precursor(s)
as small bodies (including liquid or semi-liquid bodies) on
channel-forming fibers. Upon suitable heating, particles of the
electrode composition are formed on the channel-forming fibers (or
like shapes). The entrained channel-forming fibers are removed from
their surrounding particles of electrode material to leave one or
more channels extending into or into and through the body portions
of the majority of the electrode particles. And the
channel-containing electrode particles may be utilized in a wide
range of lithium-using or sodium-using battery cells or capacitor
cells. As stated, when the channel-containing electrode particles
are immersed in a compatible liquid electrolyte for the
electrolytic cell, the electrolyte is able to contact both external
surfaces and channel surfaces of electrode particles and increase
effectiveness of the absorption and de-absorption of the lithium or
sodium into and from the electrolyte particles.
[0045] The illustration of practices of the subject invention is
not intended to limit or define the proper scope of the
invention.
* * * * *